Rb_C

Rb C-terminal domain

SMART accession number:

SM01369

Description:

The Rb C-terminal domain is required for high-affinity binding to E2F-DP complexes and for maximal repression of E2F-responsive promoters, thereby acting as a growth suppressor by blocking the G1-S transition of the cell cycle. This domain has a strand-loop-helix structure, which directly interacts with both E2F1 and DP1, followed by a tail segment that lacks regular secondary structure (PMID:16360038).

The RB C-terminal domain is required for high-affinity binding to E2F-DP complexes and for maximal repression of E2F-responsive promoters, thereby acting as a growth suppressor by blocking the G1-S transition of the cell cycle. This domain has a strand-loop-helix structure, which directly interacts with both E2F1 and DP1, followed by a tail segment that lacks regular secondary structure [(PUBMED:16360038)].

The retinoblastoma (Rb) protein negatively regulates the G1-S transition bybinding to the E2F transcription factors, until cyclin-dependent kinasesphosphorylate Rb, causing E2F release. The Rb pocket domain is necessary for E2F binding, but the Rb C-terminal domain (RbC) is also required for growthsuppression. Here we demonstrate a high-affinity interaction between RbC andE2F-DP heterodimers shared by all Rb and E2F family members. The crystalstructure of an RbC-E2F1-DP1 complex reveals an intertwined heterodimer in which the marked box domains of both E2F1 and DP1 contact RbC. We also demonstrate thatphosphorylation of RbC at serines 788 and 795 destabilizes one set of RbC-E2F-DP interactions directly, while phosphorylation at threonines 821 and 826 induces anintramolecular interaction between RbC and the Rb pocket that destabilizes theremaining interactions indirectly. Our findings explain the requirement of RbCfor high-affinity E2F binding and growth suppression and establish a mechanismfor the regulation of Rb-E2F association by phosphorylation.